Assistance Required

Hello
My first time here and hope someone can help
I have a Fiesta Finesse 03 reg with key operated central locking system and an internal tailgate release button.
Noticed yesterday the internal release didnt work and had to open tailgate externally with key.
Tried to lock car via drivers door and only that door locked (no clicks heard) had to lock passenger door separeately.
Reopened car and started engine then all seemed working ok again, but this has occurred several afterwards and again this am.
Has anyone any ideas?
regards,
Martin